Scaffolds 99 index

WAITING TO INHALE

(Art Agnello ama4@nysaes.cornell.edu, Entomology, Geneva)

It was previously believed that only white apple leafhopper (WALH), which exhibits two generations after petal fall and in mid- to late August, and potato leafhopper, which appears sporadically between these broods, depending on weather, were present in New York apples. An apparent additional brood has been noted in eastern New York between July and early August. This brood tends to overlap the late August population, so that various stages of WALH are often found on leaves throughout the summer. More recent field observations have shown that many of the leafhoppers seen in apples during midsummer may be a closely related species, rose leafhopper (RLH). An initial study of the leafhopper species complex in the Hudson Valley showed that RLH completes its first generation on weed hosts such as multiflora rose; adults begin ovipositing on apple in mid-June and nymphs appear by early July. From this time until harvest, both species are likely to be present on apple trees; usually one greatly predominates over the other, but the factors influencing the species mixture have yet to be determined. WALH (or leafhopper species complex) appears to have two fairly distinct generations in western New York. Eggs from the single summer generation usually begin to hatch from late July to early August, continuing until mid- to late August. Adults appear in late August and are active until fruit harvest.

Newly hatched White appple leafhopper nymph

White apple leafhopper adult

Nymphs and adults feed on leaves during the summer, removing chlorophyll and causing white stippling. Excrement from nymphs and adults on fruit leaves small black spots that resemble the summer disease, flyspeck. During harvest, adults fly throughout the tree canopy, annoying pickers.

Apple spotted by dried honeydew produced by white apple leafhopper feeding

Decision Making: WALH nymphs and adults are usually most common on older fruit cluster leaves inside the tree. The number of WALH on a single older fruit cluster leaf should be counted on each of 10 clusters from 5 to 10 trees. Economic threshold levels for WALH feeding damage on apples have not been developed in New York, but the thresholds suggested in other states vary from an average of 0.25 to 2 WALH nymphs and adults per leaf. Treatment for second- or third-generation WALH (or RLH mixture) is recommended in New York if an average of one or more insects (nymphs and adults) per leaf are detected. Sevin, Carzol, and Provado are all potential choices as effective insecticides with short (1—7 days) PHI's.

End of this issue: Scaffolds 1999 Index